“Another interesting point to consider (I have been trying to find some info on this) in regards to an EMP; lots and lots of older homes in the U.S. with old school plaster walls and ceiling. Inside that plaster is metal mesh; kind of like a Faraday cage.”
Even if that would work (I doubt it) only disconnected devices would be spared. Your electrical lines will bring in the pulse very nicely, and fry all attached devices.
Devices inside a metal box, such as a safe, should be fine.
Oh, completely agree, anything “plugged in” is toast. Disconnected devices might be spared in such homes, might. Like I said, I’m still reading about it.